Positive displacement rotary devices efficiently replace pistons in such uses as pumps, motors and engines. Probably the best known application is the Wankel rotary engine which was produced for Mazda automobiles. A more recent example can be found in U.S. Pat. No. 4,401,070, to McCann, which discloses a sliding vane rotary engine. And even more recently, a more general axial vane rotary device was disclosed in U.S. Pat. No. 5,429,084 (to Cherry et al.), U.S. Pat. No. 5,509,793 (to Cherry et al.), and U.S. Pat. No. 5,551,853 (to Cherry et al.).
The McCann and Cherry patents all describe rotary devices that employ oscillating axial vanes located on a rotor. Cammed surfaces or cause the axial vanes to oscillate and in conjunction with the axial vanes define increasing/decreasing volumetric spaces.
The axial vane rotary device provides an efficient replacement to piston devices by providing a positive displacement of volume. The emergence of an axial vane into a chamber on one side of a rotor corresponds to the reference piston position of Top Dead Center. The axial vane traveling around and down corresponds to a piston traveling downward in a cylinder by increasing the volume in the chamber behind the sweep of the vane. The axial vane traveling around and up and withdrawing into the rotor corresponds to a piston position of Bottom Dead Center reaching a maximum volume. The next axial vane emerging from the rotor then acts like a piston traveling upward in a cylinder to complete a compression stroke decreasing the volume as the vane sweeps around.
An advantage of rotary devices like the axial vane devices disclosed by McCann and Cherry is the lack of a return piston stroke. Without the need to reverse piston direction, this arrangement allows the axial vanes to be acted upon by pneumatic or hydraulic pressure in one continuous direction.
It is also apparent, however, that the same axial vane arrangement allows for completely reversing the operation. Reversing the shaft rotation merely changes the direction of flow through the device.
While the description above references using the axial vane device as a pump, the drive shaft of the device can also be controllable by forcing fluid flow through the device turning the axial vane device into a motor.
These axial vane devices, however, vary the resulting torque only by varying the volumes of the chambers through vertical camming. Because the chambers in the axial vane device have a constant axial width, this arrangement does not take advantage of varying the torque by varying the moment arm (i.e., varying the axial distance of the applied pressure). The axial vane devices also continue to include parts that experience reversing motions because the axial vanes oscillate up and down within the device. Further, the axial vane devices result in sharp, rectangular corners making it more difficult to seal the vanes and chambers.